The invention pertains to an improved self-aligning bearing for use in end frames of electric motor drive units and the like.
Most self-aligning bearings for small motors are of the spherical outside diameter type which add significant cost to the motor assemblies and require pre-alignment before assembly. In recent years, designs similar to those described in the assignee's U.S. Pat. No. 4,318,573 have been successfully applied. Those bearings have a bore for receiving the shaft of an electric motor and have a generally cylindrical body with some type of outwardly extending anti-rotation feature. Such anti-rotation features might be keys that are received within slots defined in the bearing socket, which requires rotational positioning of the bearing prior to assembly.
Non-self-aligning bearings have been disclosed previously which have similar anti-rotation device shapes to those suggested for this invention but those prior art features must be assembled to a non-moveable press fit. Typical examples of these types of bearings are shown in U.S. Pat. Nos. 2,376,406 and 2,989,354 wherein the anti-rotation features are a plurality of broaching projections located adjacent a leading pilot portion wherein during assembly the pilot portion is inserted in the socket allowing the bearing to align itself with the socket before the projections eventually reach the socket and shave or displace the socket wall to a tight fit. Bearings of this type require accurately located, aligned and machined sockets into which the bearings are inserted which add cost to the product. Also, because of the close fitting nature of the bearings for concentric alignment the bearings are not capable of angular displacement necessary for receiving the shaft of a rotating component not accurately aligned.
One bearing that does provide for the necessary angular displacement is shown in U.S. Pat. No. 3,115,373, however, an adhesive mounting resin is used to permanently hold the bearing in a rigid position that requires a time of setting, which, in addition to the cost of the material, adds to the manufacturing cost of the product and does not allow later realignment as necessary to accommodate disassembly and reassembly.
It is an object of the invention to provide an improved self aligning bearing that is of low manufacturing cost and permits angular displacement during assembly of parts to accommodate for bearing sockets that are not in line, such that the bearing aligns itself with its associated rotating component.
A further object of the invention is to provide a self aligning bearing to accommodate bearing sockets that are not in line wherein projections on the bearing shave or displace the socket to a precise fit by merely pressing the bearing into its associated socket.
Another object of the invention is to provide a self aligning bearing that is merely pressed into its associate socket and wherein the resulting fit is sufficient to carry the radial loads and yet allow angular displacement of the centerline of the bearing as required for self alignment during assembly and operation yet limits the angular position of the assembled bearing to assure sufficient alignment for easy assembly of a shaft into the bearing.
Yet still a further object of the invention is to provide a self aligning bearing wherein rotational positioning of the bearing prior to assembly is not required and variations in socket geometry can be tolerated.
In the preferred embodiment of the invention the self aligning bearing has a cylindrical body with a narrow band of circumferentially spaced projections extending outwardly from the outer surface and a shaft receiving bore therethrough. The projection area becomes the supporting structure for the bearing as it is received within the socket.
The ring of projections usually has an axial length of less than 50% of the outside diameter of that ring. With that geometry the incremental angular deflection of the shaft causes only small incremental radial deformation on the bearing pocket. The resulting change in radial retaining forces on the bearing are therefore so low that the tendency for the socket to urge the bearing angle of centerline toward the socket centerline is insignificant. Thus the bearing is free to align and stay aligned with the shaft. It can be appreciated that bearings with axially longer mounting surfaces relative to their diameter would not as freely align and would deliver excessive friction to the rotating shaft. An annular space adjacent to the ring of projections can be a feature of either the bearing or the socket in order to permit angular displacement of the bearing upon assembly of the rotating component not on a common centerline with the socket.